1. Field of the Invention
The present invention relates to an optical comunication part including an optical element and a holder which calks the element therein. The present invention relates to a fabricating method of an optical communication part having an optical element fixed by caking in a hollow portion of a holder.
2. Prior Art
Some optical communication part are used with optical elements fixed within hollow holders. Such parts include optical communication equipment, measuring apparatuses, optical sensors and laser devices and the like, and further, such optical elements may include lenses, mirror reflectors, waveguides, optical isolators, and optical fibers or the like. Mechanical properties, for example, tensile strength, air-tightness and solder wettability are required for the above described parts.
According to a conventional art, in the optical communication equipment many optical communication parts have been used with optical elements fixed by calking in holders or ferrules. For example, Japanese Patent Publication No. 2-262607 discloses a method for calking a cylindrical lens within a holder.
However, it may be not sufficient that the optical element is fixed within the holder without using a curable bond material but only by using calking. For example, in the case where a spherical lens and a holder have different thermal expansion coefficients, even at a temperature when using an apparatus, a gap may be formed between the lens and the holder. This involves such a defect that the lens is deviated out of position, which doses not provide a desired optical property.
Japanese Patent Publication No. 2001-290049 discloses an optical communication part having an optical fiber fixed by calking to a ferrule which is shaped in a cylinder of a metal material plastically deformable and mechanically machinable by processing such as cutting. In FIG. 22A, within the ferrule, a glass fiber in an optical fiber 127 made of quartz glass from which a two-layered coating 128 has been removed in advance is inserted in the ferrule, and part of an outside of the ferrule 125 is deformed by adding compression from the outside toward a center thereof to calk the glass fiber 127 directly.
U.S. Pat. Re. No. 36231, as shown in FIG. 22B, discloses a structure in which the shapes of an optical fiber 126 and the ferrule 125 to be used are the same as that of FIG. 22A, except that upon fixing by calking a front end of the ferrule 125 is pushed in an axial direction by a upsetting die 129 having a tapered inner surface, resulting in the front end 134 of the ferrule 125 to be deformed in a tapered form to calk the optical fiber core 127 directly therein.
On the other hand, a structure is also suggested to fix by calking the optical fiber in the ferrule with a buffer material interposed between the ferrule 125 on the inside and the fiber core 127 to be calked. In a structure shown in FIG. 22C as an example of the above, at first, a coating 128 at the front end portion of an optical fiber 126 is removed, and then, the exposed optical fiber core 127 is inserted through the ferrule 125. Japanese Patent Publication No. 2000-304968 discloses that a ferrule 125 is formed in a stepped form which is provided with a fiber core insertion hole 130 having inserted therethrough the fiber core 127 and with a coating insertion hole 131 having inserted therethrough a first coating 128a of the optical fiber 126. This structure is further provided with a coating calk portion 32 for calking the first coating 128a, and the optical fiber 126 is fixed via the first coating 128a by deforming the coating calk portion 132.
FIG. 22D shows that the coating 128 is compressed between the back end of the ferrule and the optical fiber in addition to fixing by the direct calking of the fiber core 127 at the front end of the ferrule as shown in FIG. 22B. At first, in the same manner as the above, the fiber core 127 from which the coating 128 has been removed in advance is inserted through the stepped-formed ferrule 125 and through a core insertion hole 130 at the front end of the ferrule and the coating is inserted through a coating insertion hole 131 at a rear end of the ferrule, after which the front end 134 around the fiber core and the rear end 135 of the ferrule 125 covering the coating 128 are calked respectively.
In the conventional techniques, as described above, a ferrule and a fiber core of optical fiber were directly calked, and, in calking, the outside of the ferrule was locally pressurized. However, it was very difficult in substance to deform the ferrule 125 uniformly by the force from its outer periphery. Even if the optical fiber 126 could be fixed to the ferrule, a gap was often formed between the ferrule and the fiber core which cannot ensure airtightness therebetween. On the contrary, where a calking amount is increased to secure airtightness, a crack tends to be generated in the fiber core by a calking strain directly produced thereto.
In the case of the structure as shown in FIG. 22B, it was possible to deform the front end of the ferrule 125 by the upsetting die 129 having a tapered inner shape, achieving airtightness easily, but a stress tended to be concentrated only on the front end 134 when the ferrule 125 was calked by the upsetting die 129, because the front end face of the ferrule 125 before calking was flattened at right angle to the periphery of the ferrule. Accordingly, the deformation amount of the ferrule 125 must be very minute, and the calked length 133 in FIG. 22B was not more than 0.1 mm, decreasing strength against tension between the ferrule 125 and the optical fiber 126.
Since the cross section of the front end 34 of the ferrule 125 was shaped flat, a friction force (contact resistance) against the die was so large when pressing the die 129 to the ferrule 125 that a force was not effectively transmitted in a direction toward an axis of the ferrule for calking the fiber core 127, with the ferrule 125 stressed along the axis thereof, resulting in an external diameter of the ferrule 125 to be expanded. Where the external diameter of the ferrule 125 was expanded, in installing the optical part in communication equipment, an optic axis thereof was deviated from that of its counterparts, preventing the parts from optical connecting.
In the next place, in the case of the structure as shown in FIG. 22C, when installed the part in communication equipment, the part was fixed to the other part mainly by soldering or YAG laser welding in which a high temperature was provided to the coating 28a through the ferrule 125 and the coating 128a sometimes melted to drop out the optical fiber 126 therefrom.
Because the coating 128a was of synthetic resin such as polyacrylate or polyvinyl chloride, the coating had a negative impact on the peripheral parts due to outgassing from the coating 128a in communication equipment in which the part was installed. In addition, the coating 128a was easily deteriorated by absorption of water at a high temperature and a high humidity, and was expanded or contracted due to the temperature change, the optical parts having a problem of lowering of strength and reliability to the parts. Further, variation of thickness in the coating 128a changed a gripping force after calking, which makes strength unstable.
In the structure as shown in FIG. 22D, although airtightness was ensured by directly calking the optical fiber core 127 at the front end 134 of the ferrule 125 and the tensile strength at the front end side was compensated by calking the coating 28 at the rear end 135 of the ferrule 125, when installing the optical part in communication equipment the coating 128 melted by heat in soldering or YAG laser welding in the same manner as the above described disadvantage and therefore the tensile strength of the optical fiber 26 was not secured.
The present invention has been made taking the foregoing problems into account. An object of the present invention is to provide a method for fabricating an optical communication part capable of stable calking of a holder to an optical element to effectively prevent the calked part from loosing.
Another object of the present invention is to provide a method for fabricating an optical communication part capable of being held by calking a holder certainly and uniformly to an optical element with a high reliability in strength and airtightness.
Still another object of the present invention is to provide a method for fabricating an optical communication part in which the holder is provided with a calking portion for holding a coating around the optical element, the calking portion being provided with a strong fastening force and a thermal stability.
Further another object of the present invention is to provide an optical communication part including an optical element and a hollow holder to fixing the optical element within a hollow portion thereof by calking the periphery of the hollow portion to exhibit good performances required for the optical communication parts.
The method of fabricating an optical communication part according to the present invention includes the steps of fixing an optical element in a hollow portion of a holder made of metal by calking the hollow portion of the holder, wherein the calking step include calking the holder by heating the holder to a temperature higher or cooling the holder to a temperature lower than the operating temperature of the communication part depending on whether a thermal expansion coefficient of the holder is higher or lower than that of the optical element. The part so fabricated has no gap generated between the optical element and the holder even if they are used within the operating temperature range, acquiring a desired optical property.
More in detail, when a thermal expansion coefficient of the holder is higher than that of the optical element, holding the optical element by a holding portion of the holder, the holder may be calked on the optical elemment at a higher temperature than the operating temperature of the optical communication part. On the other hand, when the thermal expansion coefficient of the holder is lower than that of the optical element, by holding this optical element by the holding portion of the holder, the holder is calked to the optical element at a lower temperature than the operating temperature of the optical communication part. In many cases, the operating temperature of the part may be in the range of xe2x88x9240xc2x0 C. to +80xc2x0 C. Further, the higher temperature in heating the holder and optical element is determined within the range of +85xc2x0 C. to +95xc2x0 C. and a lower temperature in cooling the holder and optical element when the part is fixed may be determined within the range of xe2x88x9250xc2x0 C. to xe2x88x9240xc2x0 C. When such a difference of the thermal expansion coefficient and such a range of the calking temperature can be set, the calking stress against the optical element of the holder is appropriately remained to fix the optical element at a room temperature and the operating temperature. Then it is possible to prevent the optical element from falling or dropping out of the holder, and preventing deviation of the optical axis of the optical element due to loosening the element within the holder.
A method for fixing a part by transforming the holder from the outer peripheral portion thereof toward a center of the optical element may be adopted to the above described calking. The holder may directly calk the optical fiber and the optical fiber may be calked with the coating provided to the optical fiber or the outer peripheral portion of a buffer portion provided for an outer periphery of the optical fiber or an inner follow portion of the holder.
In the fabricating method of the present invention, the optical element may include an optical fiber and a projection length of the optical fiber from a calking region where the inner surface of the holder joins the optical fiber with pressure to the front end side of the holder is defined as 1 mm or less.
According to the fabricating method of the present invention, a positioning mark may attached to the holder, and according to the calking step, a front end of the optical fiber is formed at a certain angle or at a certain position with respect to the positioning mark.
According to the fabricating method of the present invention, it in preferable that the holder may include a hollow holder body made of metal and a metal buffer layer, which is joined to the inside of the holder body through a diffusion layer.
According to the fabricating method of the present invention, it is preferable that an optical element comprises an optical fiber, and a contact length of an optical fiber in an axis direction at a calking region, to which the inner surface of the holder joins the optical fiber with pressure, is set to be 0.1 mm or more.